Various studies have conventionally been made on the influence of light, particularly sunlight, on human health. For example, it is reported that sunlight irradiation is effective against skin diseases such as a bedsore.
In the natural environment, however, the sunlight can be utilized only on sunny days and at sunny places, and its intensity differs largely depending on the season and time. In order to obtain the effect of sunlight regardless of the weather or location and with a predetermined intensity, a light therapy apparatus has been developed which emits pseudo-sunlight having a spectral distribution similar to that of sunlight.
The conventional light therapy apparatus has a spectral intensity almost coinciding with that of sunlight even in a visible light range (about 400 nm to 740 nm), and accordingly provides strong stimulation to the optic nerve and eyeball surface. It is therefore unpreferable to stare at an irradiation region or light source for long period of time. In particular, a wavelength in a near infrared range causes a burn and dryness in the surface of the irradiation region, and is accordingly unpreferable to treat a patient who does not like sunburn or an affected part with a disease such as a bedsore which should not be dried.
Also, a specific wavelength range cannot be selectively extracted and utilized, and its intensity cannot be changed.